Aluminum alloy hot forging material and method for manufacturing the same

Abstract

To provide an aluminum alloy forging material having high proof stress and capable of further improving creep characteristics.SOLUTION: An aluminum alloy forging material according to the present invention contains 0.10 mass% to 0.25 mass% of Si, 0.9 mass% to 1.3 mass% of Fe, 1.9 mass% to 2.7 mass% of Cu, 1.3 mass% to 1.8 mass% of Mg, 0.90 mass% to 1.20 mass% of Ni, 0.01 mass% to 0.10 mass% of Ti, and 0.10 mass% or less of Zn, with the remainder being Al and inevitable impurities. Further, the proof stress in a tensile test at 180°C is 220 MPa or greater and, in a DSC curve obtained by differential scanning calorimetry, the S' phase formation peak area appearing in a temperature range of 200°C to 400°C is 1.8 J / g or greater.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an aluminum alloy forging and a method for producing the same. [Background technology]

[0002] Generally, many rotating and linear components, such as engine, compressor, and turbocharger impellers, are used continuously at high temperatures, so the aluminum alloy forgings used for these components must have particularly good creep properties.

[0003] For example, Patent Document 1 discloses an aluminum alloy forging containing 0.10 to 0.25 mass% Si, 0.9 to 1.3 mass% Fe, 1.9 to 2.7 mass% Cu, 1.3 to 1.8 mass% Mg, 0.10 mass% or less Zn, 0.9 to 1.2 mass% Ni, 0.01 to 0.1 mass% Ti, and the balance being Al and unavoidable impurities. The aluminum alloy forging also specifies that the total content of Fe and Ni is 2.2 mass% or less, the total content of Mn, Cr, and Zr is 0.20 mass% or less, the average circle-equivalent diameter of the intermetallic compounds is 4.5 μm or less, and the variation in the distance between the intermetallic compounds in the ST direction is 2.3 or less. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-134414 Summary of the Invention [Problem to be solved by the invention]

[0005] However, rotating parts and linear motion parts are required to have improved resistance to higher rotation speeds and higher temperatures, and accordingly, the aluminum alloy forgings used as raw materials are required to have both better creep properties and high yield strength.

[0006] Furthermore, in recent years, achieving carbon neutrality has become a challenge for society as a whole, and there is a demand for reducing CO2 emissions even during the production of forged materials. In other words, if the heat treatment temperature and time can be reduced under various heat treatment conditions in the forged material manufacturing process, CO2 emissions can be reduced.

[0007] The present invention has been made in consideration of the above problems, and aims to provide an aluminum alloy forging that has high yield strength and further improved creep properties. Another aim of the present invention is to provide a method for producing an aluminum alloy forging that can reduce production costs, suppress CO2 emissions, and reduce the impact on global warming in the production process of the aluminum alloy forging. [Means for solving the problem]

[0008] The above object can be achieved by the following aluminum alloy forging according to the present invention (1).

[0009] (1) Si: 0.10% by mass or more and 0.25% by mass or less, Fe: 0.9% by mass or more and 1.3% by mass or less, Cu: 1.9% by mass or more and 2.7% by mass or less, Mg: 1.3% by mass or more and 1.8% by mass or less, Ni: 0.90 mass% or more and 1.20 mass% or less, Ti: 0.01% by mass or more and 0.10% by mass or less, An aluminum alloy forging comprising Zn: 0.10% by mass or less, the balance being Al and unavoidable impurities, The yield strength in a tensile test at 180°C is 220 MPa or more, An aluminum alloy forging material characterized in that, in a DSC curve obtained by differential scanning calorimetry, the area of ​​the S' phase formation peak appearing in the temperature range of 200°C or higher and 400°C or lower is 1.8 J / g or higher.

[0010] The above object can also be achieved by the following method (2) for producing an aluminum alloy forging according to the present invention.

[0011] (2) A method for producing the aluminum alloy forging according to (1), comprising the steps of: Si: 0.10 mass% or more and 0.25 mass% or less, Fe: 0.9% by mass or more and 1.3% by mass or less, Cu: 1.9% by mass or more and 2.7% by mass or less, Mg: 1.3% by mass or more and 1.8% by mass or less, Ni: 0.90 mass% or more and 1.20 mass% or less, Ti: 0.01% by mass or more and 0.10% by mass or less, a casting step of casting an aluminum alloy ingot containing 0.10% by mass or less of Zn and the remainder being Al and unavoidable impurities; a homogenization-quenching process in which the aluminum alloy ingot is subjected to homogenization heat treatment, hot forging, solution treatment, and quenching treatment; an artificial aging treatment step of performing artificial aging treatment on the quenched material after quenching, A method for producing an aluminum alloy forging, characterized in that the heating temperature in the artificial aging treatment step is 170°C or higher and 220°C or lower, and the heating time is less than 22 hours. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide an aluminum alloy forging material that has high yield strength and can further improve creep properties.

[0013] Furthermore, the present invention provides a method for producing aluminum alloy forgings that can reduce production costs, suppress CO2 emissions, and reduce the impact on global warming in the production process of aluminum alloy forgings. [Brief explanation of the drawings]

[0014] [Figure 1]FIG. 1 is a graph showing a DSC curve, with the vertical axis representing DSC (mW / mg) and the horizontal axis representing temperature T (° C.). [Figure 2] FIG. 2 is a schematic diagram showing the positions of samples collected in this example. [Figure 3A] FIG. 3A is a plan view showing a region from which a test specimen is taken from the obtained aluminum alloy forging. [Figure 3B] FIG. 3B is a side view of the aluminum alloy forging shown in FIG. 3A. [Figure 4] FIG. 4 is a graph showing the relationship between creep rupture time t and S′ phase formation peak area, with the vertical axis representing creep rupture time t and the horizontal axis representing S′ phase formation peak area. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present inventors have conducted extensive research into the relationship between aging conditions and creep properties in order to further improve the creep properties of aluminum alloy forgings. As a result, the present inventors have found that sub-aging, compared with typical peak aging, can improve creep properties. The present inventors have also found that there is a correlation between the area of ​​a peak appearing in a specific region in a DSC curve obtained by differential scanning calorimetry (DSC) for aluminum alloy forgings and creep properties. The present invention is based on these findings. Hereinafter, an aluminum alloy forging according to an embodiment of the present invention will be described in detail.

[0016] [Aluminum alloy forgings] The aluminum alloy forging according to this embodiment contains the following specific elements in predetermined content ranges. Specifically, AA2618 aluminum alloy, which has excellent high-temperature properties, can be used as the material for the aluminum alloy forging according to this embodiment. The elements contained in the aluminum alloy forging and the reasons for limiting their contents will be explained in detail below. In the following explanation, the aluminum alloy forging may be simply referred to as the forging.

[0017] (Si: 0.10 mass% or more and 0.25 mass% or less) Si, together with Mn, precipitates fine dispersed phases such as Al-Mn-Si compounds, enhances the dislocation pinning effect, and inhibits coarsening of recrystallized grains during solution treatment, thereby improving the strength of aluminum alloy forgings. If the Si content in the forgings is less than 0.10% by mass, the strength-improving effect cannot be fully achieved. Therefore, the Si content in the forgings should be 0.10% by mass or more, preferably 0.13% by mass or more, and more preferably 0.15% by mass or more, based on the total mass of the forgings.

[0018] On the other hand, if the Si content in the forged material exceeds 0.25% by mass, compounds of Mg and Si are formed, resulting in a decrease in heat resistance. Therefore, the Si content in the forged material is set to 0.25% by mass or less, preferably 0.23% by mass or less, and more preferably 0.21% by mass or less, based on the total mass of the forged material.

[0019] (Fe: 0.9 mass% or more and 1.3 mass% or less) Fe forms Fe-Ni compounds together with Ni, and has the effect of improving the heat resistance of aluminum alloy forgings. If the Fe content in the forgings is less than 0.9 mass%, the effect of improving the heat resistance of the forgings cannot be sufficiently obtained. Therefore, the Fe content in the forgings is set to 0.9 mass% or more, and preferably 1.0 mass% or more, based on the total mass of the forgings.

[0020] On the other hand, if the Fe content in the forged material exceeds 1.3 mass%, Fe-based compounds such as Al-Fe and Al-Fe-Cu compounds are significantly formed and dispersed in the matrix, reducing the effect of improving heat resistance. Therefore, the Fe content in the forged material is set to 1.3 mass% or less, and preferably 1.2 mass% or less, based on the total mass of the forged material.

[0021] (Cu: 1.9 mass% or more and 2.7 mass% or less) Cu has the effect of improving the strength of aluminum alloy forgings at room temperature and high temperatures. Specifically, by including a predetermined amount of Cu in the forgings, both solid solution strengthening and precipitation strengthening effects can be obtained, thereby ensuring the high-temperature yield strength and heat resistance required in this embodiment. More specifically, Cu combines with Al and Mg during high-temperature artificial aging treatment to precipitate GPB zones and S' phases finely and densely, thereby improving the strength of the forgings after artificial aging treatment. The S' phase will be described later.

[0022] If the Cu content in the forged material is less than 1.9% by mass, the effect of improving the strength of the forged material cannot be fully achieved. Therefore, the Cu content in the forged material is set to 1.9% by mass or more, preferably 2.0% by mass or more, and more preferably 2.1% by mass or more, based on the total mass of the forged material. On the other hand, if the Cu content in the forged material exceeds 2.7% by mass, the eutectic melting start temperature decreases, and the solution treatment temperature must be lowered. This reduces the amount of Cu dissolved in the matrix, and the effect of improving the strength of the forged material cannot be achieved. Therefore, the Cu content in the forged material is set to 2.7% by mass or less, preferably 2.6% by mass or less, and more preferably 2.5% by mass or less, based on the total mass of the forged material.

[0023] (Mg: 1.3 mass% or more and 1.8 mass% or less) Mg, in combination with Cu, has the effect of improving the strength of aluminum alloy forgings at room temperature and at high temperatures. Specifically, by including a predetermined amount of Mg in the forgings, both solid solution strengthening and precipitation strengthening effects can be obtained, thereby ensuring the high-temperature yield strength and heat resistance required in this embodiment. More specifically, Mg combines with Al and Cu during high-temperature artificial aging to precipitate GPB zones and S' phases finely and densely, thereby improving the strength of the forgings after artificial aging.

[0024] If the Mg content in the forged material is less than 1.3% by mass, the effect of improving the strength of the forged material cannot be sufficiently obtained. Therefore, the Mg content in the forged material is set to 1.3% by mass or more, preferably 1.4% by mass or more, and more preferably 1.5% by mass or more, based on the total mass of the forged material. On the other hand, if the Mg content in the forged material exceeds 1.8% by mass, the deformation resistance of the material increases during hot working such as forging, reducing productivity. Therefore, the Mg content in the forged material is set to 1.8% by mass or less, preferably 1.7% by mass or less, and more preferably 1.6% by mass or less, based on the total mass of the forged material.

[0025] (Ni: 0.90 mass% or more and 1.20 mass% or less) Ni forms Fe-Ni compounds together with Fe, and has the effect of improving the heat resistance of aluminum alloy forgings. If the Ni content in the forgings is less than 0.90 mass%, the effect of improving heat resistance cannot be sufficiently obtained. Therefore, the Ni content in the forgings is set to 0.90 mass% or more, preferably 0.95 mass% or more, and more preferably 1.00 mass% or more, based on the total mass of the forgings.

[0026] On the other hand, if the Ni content in the forged material exceeds 1.20 mass%, Ni-based compounds such as Al-Ni and Al-Ni-Cu compounds are formed dispersed in the matrix, reducing the effect of improving heat resistance. Furthermore, coarse Fe-Ni and other intermetallic compounds are formed, making cracks more likely to occur during hot working such as forging, reducing productivity. Therefore, the Ni content in the forged material should be 1.20 mass% or less, preferably 1.18 mass% or less, and more preferably 1.10 mass% or less, based on the total mass of the forged material.

[0027] (Ti: 0.01 mass% or more and 0.10 mass% or less) Ti is a component contained in the forged material to stably obtain a fine grain structure. If the Ti content in the forged material is less than 0.01 mass%, the effect of stabilizing the fine grain structure cannot be sufficiently obtained. Therefore, the Ti content in the forged material is set to 0.01 mass% or more, and preferably 0.04 mass% or more, based on the total mass of the forged material.

[0028] On the other hand, if the Ti content in the forged material exceeds 0.10 mass%, large Al-Ti compounds are formed during casting, resulting in a decrease in strength. Therefore, the Ti content in the forged material is set to 0.10 mass% or less, and preferably 0.09 mass% or less, based on the total mass of the forged material.

[0029] (Zn: 0.10% by mass or less) Zn is an element that is often contained in forged materials as an unavoidable impurity. Zn also has the effect of improving the room-temperature and high-temperature strength of aluminum alloy forged materials through solid-solution strengthening and precipitation strengthening. However, since the effect of improving the room-temperature and high-temperature strength of aluminum alloy forged materials can be sufficiently obtained by Cu and Mg, Zn does not necessarily need to be contained in the forged material.

[0030] Furthermore, if the Zn content in the forged material exceeds 0.10 mass%, the corrosion resistance of the forged material decreases. Therefore, the Zn content in the forged material is set to 0.10 mass% or less, preferably 0.09 mass% or less, more preferably 0.08 mass% or less, and even more preferably 0.05 mass% or less, based on the total mass of the forged material.

[0031] (Remainder: Al and inevitable impurities) The balance of the aluminum alloy forging according to this embodiment is Al and unavoidable impurities. The unavoidable impurities are inevitably contained due to the raw materials used in actual production. In addition to Zn, examples of the unavoidable impurities include Mn, Cr, Zr, and V. Of these unavoidable impurities, V is preferably 0.05% by mass or less relative to the total mass of the forging. The total content of Mn, Cr, and Zr is preferably 0.20% by mass or less, and more preferably 0.15% by mass or less, relative to the total mass of the forging. As long as the V content and the total content of Mn, Cr, and Zr do not exceed the upper limit values ​​described in this embodiment, the effects of the present invention are not hindered even when they are contained as unavoidable impurities or when they are intentionally contained.

[0032] (0.2% yield strength in tensile tests at 180°C: 220 MPa or more) The aluminum alloy forging according to this embodiment aims to achieve even better creep properties than conventional forgings. For example, in the aluminum alloy forging described in Patent Document 1, the creep properties (time until fracture of a test specimen) at a temperature of 180°C and a load stress of 220 MPa are at most 284.6 hours. Therefore, in this embodiment, creep properties better than those of conventional products, i.e., the target creep properties, are set to 290 hours or more. To achieve this creep property, the forging needs to have a 0.2% yield strength of 220 MPa or more when subjected to a tensile test at 180°C. Therefore, the aluminum alloy forging should have a 0.2% yield strength of 220 MPa or more in a tensile test at 180°C, preferably 250 MPa or more, and more preferably 280 MPa or more. The 0.2% proof stress in a tensile test at 180°C can be measured, for example, in accordance with JIS G0567:2020 "High-temperature tensile test method for steel materials and heat-resistant alloys" using a flanged test piece described in Appendix A.

[0033] (S' phase formation peak area: 1.8 J / g or more) Generally, when differential scanning calorimetry (DSC) is performed on aluminum alloy materials, an upward convex exothermic peak is observed due to the precipitation phenomenon of precipitates of a few nanometers in size. It is also known that a downward convex endothermic peak is observed due to solid solution (dissolution) (Reference 1: Akikazu Maezono, Light Metals, vol. 51, No. 9, (2001), 464-476. Reference 2: Taichi Suzuki, Hideaki Hatta, Hideo Yoshida, Light Metals, vol. 68, No. 7, (2018), 333-338.).

[0034] 1 is a graph showing a DSC curve, with the vertical axis representing DSC (mW / mg) and the horizontal axis representing temperature T (° C.) The analysis conditions for the graph in FIG. 1 are as follows: Equipment used: Therma plus EVO2 high-sensitivity differential scanning calorimeter DSC8231 (Rigaku Corporation) ·Heat flux DSC device (JIS K 0129:2005) Measurement conditions: From room temperature (approx. 25°C) to 530°C in a nitrogen gas atmosphere at a heating rate of 10°C / min. Sample: Approximately 20 mg used Reference: Al2O3 powder

[0035] As shown in Figure 1, in the aluminum alloy forging according to this embodiment, DSC measurement reveals an exothermic peak C for S' phase formation within the temperature range of 200 to 400°C. The S' phase is an intermediate layer (metastable phase) that is thought to precipitate after the GPB zone, and has a lath-like morphology and an orthorhombic structure with a = 4.0 Å, b = 9.2 Å, and c = 7.1 Å, with the precipitation plane being the {210} plane. <100> The matrix phase is a compound that is partially coherent to semi-coherent and easily nucleates on dislocation loops. This S' phase is a precipitate phase that contributes to improving strength, and although no clear chemical formula has been reported, the stable S phase is considered to be a compound of CuMgAl2. In this embodiment, the area of ​​the S' phase formation peak that appears in the temperature range of 200°C to 400°C in the DSC curve obtained by DSC is specified.

[0036] The S' phase formation peak area will be further explained using Figure 1. The peak (S' phase formation peak) that appears in the temperature range of 200°C or higher and 400°C or lower is defined as exothermic peak C, and the peak adjacent to exothermic peak C via endothermic peak B on the lower temperature side is defined as exothermic peak A. In this specification, the area per unit heating rate (°C / s) of the shaded region surrounded by exothermic peak C and an auxiliary line that passes through the apex of exothermic peak A and is parallel to the x-axis is defined as the "S' phase formation peak area."

[0037] If the S' phase formation peak area in the forged material is less than 1.8 (J / g), the desired creep properties cannot be obtained. Therefore, the S' phase formation peak area is set to 1.8 (J / g) or more. On the other hand, there is no particular upper limit for the S' phase formation peak area, but when measuring an as-quenched sample (before the artificial aging treatment described below), which is likely to have the largest S' phase formation peak area, it is 7.4 (J / g). Therefore, it is preferable that the S' phase formation peak area in the forged material be 7.4 (J / g) or less.

[0038] Next, a method for producing an aluminum alloy forging according to an embodiment of the present invention will be described.

[0039] [Manufacturing method for aluminum alloy forgings] The method for producing an aluminum alloy forging according to this embodiment includes a casting step of casting an aluminum alloy ingot having a predetermined composition, a homogenization-quenching step of subjecting the resulting aluminum alloy ingot to a homogenization heat treatment, hot forging, solution treatment, and quenching, and an artificial aging treatment step of subjecting the quenched material to an artificial aging treatment. Each step will be described in more detail below.

[0040] <Casting process> The casting process is a process of casting a molten metal melted to a predetermined composition to produce an aluminum alloy ingot. The aluminum alloy ingot contains predetermined amounts of Si, Fe, Cu, Mg, Ni, and Ti, a Zn content of a predetermined value or less, and the balance consisting of Al and unavoidable impurities. The contents of each element in the aluminum alloy ingot and the reasons for limiting the numerical values ​​are the same as those for each element in the aluminum alloy forging, and are as described above. The casting method and the shape of the ingot are not particularly limited, and conventional methods and shapes can be used.

[0041] <Homogenization-quenching process> Next, the aluminum alloy ingot obtained by the casting process is subjected to homogenization heat treatment, hot forging, solution treatment, and quenching. The temperature rise rate and holding temperature of the homogenization heat treatment are not particularly limited, and general conditions can be used. The temperature rise rate of the homogenization heat treatment can be, for example, 5°C / min or less, and the holding temperature can be, for example, 450 to 550°C. The start temperature and end temperature of the hot forging are also not particularly limited, and general conditions can be used. The start temperature of the hot forging can be, for example, 350 to 500°C, and the end temperature can be, for example, 300 to 500°C. The holding temperature, holding time, and temperature rise rate of the solution treatment are also not particularly limited, and general conditions can be used. The holding temperature of the solution treatment can be, for example, 520 to 570°C, the holding time can be, for example, 20 minutes to 20 hours, and the temperature rise rate can be, for example, 100°C / hour or more. Quenching is a treatment process in which the material after solution treatment is cooled by immersing it in water or hot water. The cooling rate is not particularly limited, and general conditions can be used. The cooling rate in quenching can be, for example, 40°C / second or more.

[0042] <Artificial aging treatment process> The artificial aging process is a process in which the quenched material obtained by the quenching process is subjected to artificial aging. As described above, in this embodiment, the artificial aging process is performed under sub-aging conditions to improve the creep properties of the forged material. In other words, it is important to select heat treatment conditions before peak aging. The sub-aging conditions are determined by appropriately selecting the balance between heating temperature and heating time. For example, a general heating temperature range can be applied, and a heating time shorter than the general heating time can be selected.

[0043] If the heating temperature in the artificial aging treatment step is less than 170°C, the forged material cannot be sufficiently hardened. Therefore, the heating temperature in the artificial aging treatment step is set to 170°C or higher, preferably 180°C or higher, and more preferably 190°C or higher. On the other hand, if the heating temperature in the artificial aging treatment step exceeds 220°C, the condition for under-aging is not met, making it difficult to improve creep properties. Therefore, the heating temperature in the artificial aging treatment step is set to 220°C or lower, preferably 210°C or lower, and more preferably 200°C or lower.

[0044] If the heating time in the artificial aging treatment step is 22 hours or more, the condition for sub-aging will not be met, making it difficult to improve creep properties. Therefore, the heating time in the artificial aging treatment step is set to less than 22 hours. [Example]

[0045] The present embodiment will be described in more detail below with reference to examples, but the present invention is not limited to these examples, and modifications can be made within the scope of the spirit of the present invention, and all such modifications are included in the technical scope of the present invention.

[0046] <Manufacturing of aluminum alloy forgings> (Casting process) FIG. 2 is a schematic diagram showing the location of samples taken in this example. An iron mold 11 was prepared, having a cylindrical shape with a bottom smaller than the diameter of the opening. Molten aluminum alloy having a predetermined composition was poured into the mold 11 to produce an ingot 12 by metal mold casting. The resulting ingot 12 had a mass of approximately 5.5 kg. The ingot 12 was then removed from the mold 11, cut, and machined to produce a cylindrical sample 13 from approximately the center of the ingot 12. The size of the sample 13 was 100 mm in diameter and 120 mm in height. In this example, the mass of the ingot 12 was approximately 5.5 kg. However, the ingot is not limited to this size. For example, an ingot weighing 2 tons or more can also be used to produce an aluminum alloy forging under similar conditions as described below.

[0047] (Homogenization-quenching process) Sample 13 was then placed in an air furnace and subjected to homogenization heat treatment at a temperature of 520°C for 20 hours, after which it was cooled to room temperature. Sample 13 was then placed in an air furnace again and heated to 300-340°C, after which it was removed from the furnace and hot forged using a hydraulic forging press. The hot-forged material was then placed in an air furnace and subjected to solution treatment at a temperature of 530°C for 6 hours, after which it was quenched in boiling water to obtain a quenched material.

[0048] (Artificial aging treatment process) The quenched material after the homogenization and quenching process was then placed in an air furnace and artificially aged at 197°C for the times shown below to obtain T61-treated aluminum alloy forgings. In the present examples, the artificial aging treatment time for Inventive Example No. 1 was 16 hours, which was a treatment condition for under-aging. The artificial aging treatment time for Comparative Example No. 1 was 22 hours, which was a treatment condition for peak aging. The artificial aging treatment time for Comparative Example No. 2 was 36 hours, which was a treatment condition for over-aging.

[0049] FIG. 3A is a plan view showing a region from which test specimens were taken from the obtained aluminum alloy forging, and FIG. 3B is a side view of the aluminum alloy forging shown in FIG. 3A. The disk-shaped aluminum alloy forging 21 had a diameter of 200 mm in the rolling direction (L direction) and a thickness of 30 mm in the plate thickness direction (ST direction). In FIGS. 3A and 3B, the hatched areas indicate the region 22 from which test specimens were taken. Specifically, test specimens for tensile tests and creep tests were taken from the center of the plate thickness of the aluminum alloy forging 21 and the region 22 extending radially from near the center of the disk shape.

[0050] <Evaluation of aluminum alloy forgings> Measurement by DSC, tensile test and creep test were carried out using test pieces taken from the obtained aluminum alloy forgings 21. In addition, the electrical conductivity of the obtained aluminum alloy forgings 21 was measured.

[0051] (Calculation of S' phase formation peak area) A sample for DSC measurement was taken from the chuck of a test piece for a tensile test taken from the aluminum alloy forging 21, and DSC measurement was carried out. Then, the S' phase formation peak area that appeared in the temperature range of 200 to 400°C was calculated. The measurement conditions were as follows. Equipment used: Therma plus EVO2 high-sensitivity differential scanning calorimeter DSC8231 (Rigaku Corporation) ·Heat flux DSC device (JIS K 0129:2005) Measurement conditions: From room temperature (approx. 25°C) to 530°C in a nitrogen gas atmosphere at a heating rate of 10°C / min. Sample: Approximately 20 mg used Reference: Al2O3 powder

[0052] (Tensile test) In accordance with JIS G 0567:2020 "High temperature tensile test method for steel materials and heat-resistant alloys," tensile tests were conducted at 180°C using flanged test pieces described in Appendix A, and the tensile strength, 0.2% yield strength, and elongation after fracture were measured.

[0053] (Creep test) In accordance with JIS Z 2271:2010 "Methods for creep and creep rupture testing of metallic materials," creep rupture times were measured at a temperature of 180°C under a load of 220 MPa. A creep rupture time of 290 hours or more was judged to have a good creep test result (○). A creep rupture time of less than 290 hours was judged to have a poor creep test result (×).

[0054] (Conductivity measurement) The obtained aluminum alloy forging 21 was cut at a desired position, and the exposed cross section was mechanically polished to #2000, and the conductivity of the resulting surface was measured. The conductivity was measured at room temperature (approximately 25°C) by pressing the tip of a conductivity meter probe against the sample. Note that, as long as the measurement surface is relatively smooth, the conductivity can be measured using any desired polishing roughness. The equipment used to measure the conductivity is shown below. Equipment used: Conductivity meter SIGMASCOPE SMP350 (manufactured by Fisher Instruments) Applicable standards: ASTM E1004, etc.

[0055] The contents of each component contained in the aluminum alloy forgings and the heating conditions in the artificial aging treatment process are shown in Table 1 below, and the measurement results of each test are shown in Table 2 below.

[0056] [Table 1]

[0057] [Table 2]

[0058] Figure 4 is a graph showing the relationship between creep rupture time and S' phase formation peak area, with the vertical axis representing creep rupture time t and the horizontal axis representing S' phase formation peak area. As shown in Tables 1 and 2 and Figure 4, Example 1 forged material contained components within the ranges specified by the present invention, and the heating temperature and time in the artificial aging process were appropriately controlled, resulting in under-aging. As a result, the S' phase formation peak area was 1.8 J / g or more, the 0.2% proof stress at a high temperature of 180°C was 220 MPa, and the creep rupture time was 290 hours or more. Furthermore, because the heating time in the artificial aging process could be set shorter than conventional methods, manufacturing costs were reduced, CO2 emissions were suppressed, and the impact on global warming was mitigated.

[0059] On the other hand, in Comparative Examples Nos. 1 and 2, the heating conditions in the artificial aging treatment step were such that peak aging or overaging occurred, and therefore the desired creep properties could not be obtained. [Explanation of symbols]

[0060] 11 Mold 12 Ingot 13 Sample 21 Aluminum alloy forgings

Claims

1. Si: 0.10% by mass or more and 0.25% by mass or less, Fe: 0.9% by mass or more and 1.3% by mass or less, Cu: 1.9% by mass or more and 2.7% by mass or less, Mg: 1.3% by mass or more and 1.8% by mass or less, Ni: 0.90% by mass or more and 1.20% by mass or less, Ti: 0.01% by mass or more and 0.10% by mass or less; Zn: 0.10% by mass or less, the balance being Al and unavoidable impurities, The yield strength in a tensile test at 180 ° C is 220 MPa or more, An aluminum alloy forging material characterized in that, in a DSC curve obtained by differential scanning calorimetry, the area of ​​an S' phase formation peak appearing in the temperature range of 200°C or higher and 400°C or lower is 1.8 J / g or higher.

2. A method for producing the aluminum alloy forging according to claim 1, comprising: Si: 0.10% by mass or more and 0.25% by mass or less, Fe: 0.9% by mass or more and 1.3% by mass or less, Cu: 1.9% by mass or more and 2.7% by mass or less, Mg: 1.3% by mass or more and 1.8% by mass or less, Ni: 0.90% by mass or more and 1.20% by mass or less, Ti: 0.01% by mass or more and 0.10% by mass or less; a casting step of casting an aluminum alloy ingot containing Zn: 0.10% by mass or less, with the balance being Al and unavoidable impurities; a homogenization-quenching process in which the aluminum alloy ingot is subjected to homogenization heat treatment, hot forging, solution treatment, and quenching treatment; an artificial aging treatment step of performing artificial aging treatment on the quenched material after quenching, The method for producing an aluminum alloy forging is characterized in that the heating temperature in the artificial aging treatment step is 170°C or higher and 220°C or lower, and the heating time is less than 22 hours.

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